Knee replacements are preformed through an incision on the front of the knee. There are some different ways to handle the soft tissue and extensor mechanism of the knee which are discussed below. Each approach has advantages and disadvantages.
Medial Parapatellar Approach
A medial parapatellar incision involves cutting the quadriceps tendon above the knee cap (patella) and around the inside (medial) of the knee cap. The tendon is then repaired at the end of the procedure. The idea behind cutting the tendon is that the tendon might heal better than cutting into the muscle belly of the VMO. The patella is typically flipped during this approach to gain access to the knee joint which may or may not affect the knee rehab in the short term.
A mid-vastus approach does not cut the quadriceps tendon but instead cuts into the VMO muscle belly and around the inside of the knee cap. The idea behind leaving a large portion of the VMO attached to the quadriceps is that the VMO muscle may help patellar tracking and knee extension strength. The muscle belly is repaired at the end of the procedure. The patella may or may not be flipped during this approach.
The sub-vastus approach elevates the VMO muscle instead of cutting into it. The incision then extends around the inside of the knee cap. The patella is typically not flipped with this approach. This approach is difficult in muscular patients with large VMO muscles and generally makes the operation a little harder. Theoretically, the patella tracking and quadriceps muscle strength may be temporarily improved with this approach in the short term, but there are no long term differences months later.
The quad-sparing approach cuts just the inside of the knee cap. This approach requires special side cutting instruments. There is definitely a steep learning curve regarding the use of these instruments and many physicians (including myself) worry about the accuracy of the bone cuts and limb alignment with these side cutting instruments. This approach has received some press, but has not caught on among orthopedic surgeons.
Lateral parapatellar Approach
The lateral parapatellar approach is a uncommon approach where the incision extends around the outside (lateral) of the knee cap. Some surgeons will use this approach for severe valgus deformities.
Good results after a total knee replacement can be achieved with any of the above approaches. Patients should allow the surgeon to perform the approach the surgeon is most comfortable with.